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Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 14
CHARACTERISTICS
1. Drivers' characteristics
a) Driving task: القیادة مھمة
By keeping the vehicle at a desired speed and position with a lane, interaction
with other traffic, and reading guide signs.
b) Vision: الرؤیة
1. Visual acuity البصر حدة
2. Peripheral vision المحیطیة الرؤیة
3. Colour vision اللون رؤیة
4. Depth perception ابعاد بثلاثة الاجسام ادراك على البصریة القدرة( العمیق الادراك )
5. Hearing perception
c) Perception-reaction time (P.I.E.V): الفعل رد زمن – الادراك
1. Perception (seeing the stimuli) المحفزات رؤیة( الادراك )
2. Interpretation (understanding the stimuli) المحفزات فھم – ترجمة
3. Evaluation of appropriate response (i.e., decision) المناسبة الاستجابة تقییم
4. Volition or response (i.e., apply the reaction) الاستجابة او القرار
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 15
P.I.E.V. Refers to the time taken to detect the target, identify the target, decide on
response and initiate the response. Perception-reaction time does not include the
time to execute the decision (e.g. stop by applying a brake). The perception-
reaction time is not fixed for all drivers and also changes for a same driver depend
on the situations.
Factors affecting perception-reaction time
1. Age العمر
2. Fatigue الاجھاد
3. Complexity of Cues الدلائل( الاشارات تعقید )
4. Presence of Drugs or Alcohol الكحول او المخدرات تعاطي
5. Expectation التنبأ( التوقع )
Complexity of Cues
2. Pedestrian characteristics
Same characteristics of drive with addition of others witch influent the design and
location of the pedestrian control devices such as:
1. Special pedestrian signals.
2. Safety zones and islands at intersections.
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 16
3. Pedestrian underpasses.
4. Elevated walkways.
5. Crosswalks.
all-red ال طور تصمیم ان مثلا, السیطرة وسائل تصمیم في مباشر تاثیر لھا العبور في المشاة ممیزات
سرعة معرفة یتطلب حیث للیسارات الكثیف المرور خلال التقاطعات في الاشخاص لمرور یسمح والذي
.النفسیة والحالة التعلم ودرجة والذكاء والجنس العمر حسب تختلف قد والتي للاشخاص المشي
3. Vehicle characteristics
Criteria for the geometric design of highways are partly based on:
A. Static characteristics
Height, Width, Length and Minimum and Maximum Turning Radii as they
control of payment design
B. Kinematic characteristics
Involve the movement of the vehicle without considering the forces that causes
the motion such as acceleration capability of the vehicle, braking, turning,…….
C. Dynamic characteristics
Involve the forces that causes the motion of the vehicle:
1. Air resistance
2. Grade resistance
3. Rolling resistance
4. Curve resistance
5. Friction resistance
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 17
Vehicle performance
Vehicle performance is defined by how well a vehicle can accelerate, decelerate,
brake and maneuver.
Vehicle types
In general, there are three common types of vehicles, these are:
1. Passenger cars
Passenger cars are two-axle, four-tires, generally with seating for two to six
passengers.
2. Trucks
Vehicles with at least two-axle and six tires, and have a cargo area. Trucks are
used for commercial goods transportation.
3. Buses
Buses are designed to carry passengers and have more than four tires.
4. Road characteristics
The characteristics that affects on :
Stopping sight distance للوقوف الرؤیة مجال
Passing sight distance للتجاوز الرؤیة مجال
These characteristics are:
a) Gradient
b) Superelevation
c) Geometric design of the road
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 18
Examples:
Vehicle time headways and spacing were measured at a point along a highway,
from a single lane, for an hour. The average values were calculated as 2 .5 s for
headway and 61 m for spacing . Calculate the average speed of the traffic.
Average speed = spacing / headway
= (61/1000) / (2.5/3600)
= 87.84 km/h
Or
q = 3600/ha
= 3600/ 2.5= 1440 veh
Density = 1000 / 61 = 16.39
Average speed = q/D
= 1440 / 16.39 = 87.85 km / h
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 19
Examples 1:
An observer counts 360 veh/h at a specific highway location. Assuming that the
arrival of vehicles at this highway location is Poisson distributed, estimate the
probabilities of having 0, 1, 2, 3, 4, and 5 or more vehicles arriving over a 20-
second time interval .
SOLUTION
The average arrival rate, 20, is 360 veh/h, or 0.1 vehicles per second (veh/s) .
Using t = 20 seconds, the probabilities of having exactly 0, 1, 2, 3, and 4
vehicles arrive are:
For five or more vehicles,
P(5)=1—P(n<5 )
=1— 0.135 — 0.271 — 0.271 — 0.180 — 0.090
= 0 .053
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 20
A histogram of these probabilities is shown in Figure
Number of vehicles arriving in a 20-s time interval
(probabilities in parentheses)
Example 2:
Traffic data are collected in 60-second intervals at a specific highway location
as shown in Table 1 . Assuming the traffic arrivals are Poisson distributed and
continue at the same rate as that observed in the 15 time periods shown, what is
the probability that six or more vehicles will arrive in each of the next three 60-
second time intervals (12 :15 P .M . to 12 :16 P.M., 12 :16 P.M. to 12 :17 P.M.,
and 12 :17 P.M. to 12 :18 P.M.)?
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 21
Table 1 shows that a total of 101 vehicles arrive in the 15-minute period from
12 :00 P .M . to 12 :15 P .M . Thus the average arrival rate, λ, is 0.112 veh/s
(101/900) . Then find the probabilities of exactly 0, 1, 2, 3, 4, and 5 vehicles
arriving. Applying Poisson Eq, with λ =0.112 veh/s and t = 60 seconds, the
probabilities of having 0, 1, 2, 3, 4, and 5 vehicles arriving in a 60-second time
interval are (using AAR = 6.733) { λ t =0.112*60} 0r {101/15}
Table 1 Observed Traffic Data for Example
No Time period Observed number of vehicles
1 12 :00 P .M . to 12 :01 P .M . 3
2 12 :01 P.M. to 12 :02 P.M. 5
3 12 :02 P .M . to 12 :03 P .M . 4
4 12 :03 P .M . to 12 :04 P.M. 10
5 12 :04 P.M. to 12 :05 P.M. 7
6 12 :05 P.M. to 12 :06 P.M. 4
7 12 :06 P.M. to 12 :07 P.M. 8
8 12 :07 P.M. to 12 :08 P.M. 11
9 12:08 P .M . to 12 :09 P.M. 9
10 12:09 P .M . to 12 :10 P.M. 5
11 12:10 P .M . to 12 :11 P.M. 3
12 12:11 P .M . to 12 :12 P .M . 10
13 12:12 P .M . to 12 :13 P.M. 9
14 12:13 P .M . to 12 :14 P.M. 7
15 12:14 P .M . to 12 :15 P.M. 6
Total 15 Minutes 101
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 22
The summation of these probabilities is the probability that 0 to 5 vehicles will
arrive in any given 60-second time interval, which is: = 0.0012+0.008+0.027+0.0606+0.102+0.137 = 0 .3358
So 1 minus P(n≤5) is the probability that 6 or more vehicles will arrive in any
60-second time interval, which is
P(n≥6)=1- P(n≤5)
=1-0.3358
= 0 .6642
The probability that 6 or more vehicles will arrive in three successive time
intervals (t1 , t2 , and t3) is simply the product of probabilities, which is:
P(n≥6) for three successive time periods = (0.6642)^3
= 0.293
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 23
Example 3: Five vehicles, as shown in the figure below, are traveling at
constant speeds on section of 230m length. Assuming that all vehicles have a
same length of 4m and if speeds and clear spacing between vehicles are as
shown in the figure, estimate the following:
1. Traffic density
2. Average time headway arriving a section A-A
3. Average clear spacing
Traffic density D = (veh/km) = (푁표.표푓 푣푒ℎ푖l푒푠 표푛 푎 푠푒푔푚푒푛푡/ 푙푒푛푔푡ℎ 표푓 푡ℎ푒 푠푒푔푚푒푛푡 (푘푚)) = 5/0.23 = 21.7 veh/km Estimation of average time headway: Arrival of vehicle 2 (t2)=(30+4)/(76*1000/3600)=1.61 sec Headway of vehicle 2 (h2)=1.61 Arrival of vehicle 3 (t3) =(80+8)/(75*1000/3600)=4.224 Headway of vehicle 3 (h3)=4.224-1.61=2.614 sec Arrival of vehicle 4 (t4)= (140+12)/(80*1000/3600)=6.84sec Headway of vehicle 4 (h4)=6.84-4.224=2.616sec Arrival of vehicle 5 (t5)= (175+16)/(75*1000/3600)=9.168 Headway of vehicle 5 (h5)=9.168-6.84=2.232sec Average time headway=(1.61+2.614+2.616+2.232)/4 = 2.268sec Average clear spacing=(30+50+60+35)/4=43.75m
Civil Engineering Department TRAFFIC ENGINEERING Third Year 2018
Lecturer: Dr. Mohammed Bally Mahdi 24
Example 4:
The number of traffic accidents that occurs on a particular stretch of road during
a month follows a Poisson distribution with a mean of 9.4. Find the probability
that less than two accidents will occur on this stretch of road during a randomly
selected month.
푃(푋 = 0) = e . ( . )
! = 0.0000827
푃(푋 = 1) = e . ( . )!
= 0.00078
P(x < 2) = P(x = 0) + P(x = 1) = 0.000860
푃(푋 = x) = e−푚 (푚)푥
푥!